(Invited) The Effect of Surfactants on Vanadium Electrochemistry in Porous Carbon Electrodes

Abstract

We present a study of vanadium electrochemistry in porous electrodes with and without sodium dodecyl sulfate (SDS) additives present. Carbon paper and felt electrodes are compared. Carbon felt electrodes are the de facto standard in flow batteries. There are significant differences in the electronic conductivity of these media. The carbon paper has a much higher conductivity than the felt, which has an electronic conductivity similar to the ionic conductivity of the electrolytes used. The latter fact motivates an extension of available theory for polarization curve fitting to explicitly include both electronic and ionic contributions in the porous electrode. We demonstrate agreement between our model and an existing model evaluated at the limit where electrode conductivity is significantly greater than electrolyte conductivity. Our model uses the product of the electrode surface area per volume ratio and the heterogeneous electron transfer rate constant, and the Damköhler number as fitting parameters for carbon paper and felt electrodes. We discuss the effect of SDS additives on kinetics in the context of the cation hydration shell for the vanadium ions. To this point, we apply Marcus-Hush-Chidsey formalism to our porous electrode model to quantify reorganization energies obtained through polarization curve fitting. This work was supported as part of the Breakthrough Electrolytes for Energy Storage (BEES2), an Energy Frontier Research Center funded by the United States. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0019409.